The present invention relates to a method for producing a ferrous sintered alloy, and to a ferrous sintered alloy product applied to a vane used in a rotary compressor available for an air conditioner and an air cooling device.
A structure of an ordinary rotary compressor provided with an eccentric rotor is shown in FIG. 1. In FIG. 1, a rotor housing 2 is disposed in a casing 1, and the rotor housing 2 is formed with a vane groove 3 in the radial direction thereof. A vane 4 is disposed slidable with respect to the vane groove 3. In the rotor housing 2, a rotor 5 is rotatably disposed. The rotor 5 is fitted with a crankshaft 6 whose rotation shaft 6a is provided coaxial with the rotor housing 2, and whose crank portion 6b is disposed eccentrical with respect to the rotation shaft 6a. A radially inner end of the vane 4 is in sliding contact with the outer peripheral surface of the rotor 5, and a radially outer end of the vane 4 is connected to a coil spring 9 disposed in a recess 10 of the rotor housing 2. Therefore, the vane 4 is urged radially inwardly by the spring 9, so that the inner end of the vane is in continuous contact with the rotor 5. Upon rotation of the rotor 5, the vane Is reciprocally movable along the vane groove 3, and fluid intake and discharge operation is performed. The vane 4 fluid-tightly divides a cavity of the rotor housing 2 into two chambers as shown.
In this connection, the vane must provide sufficient fluid tightness to positively partition the two pressure chambers. Further, the vane 4 must provide high wear resistivity due to sliding contact with the rotating rotor 6.
Recently, there has been produced a vane for use in the rotary compressor made of a sintered alloy formed primarily of ferrous powders so as to obtain a resultant vane having high wear resistance and fluid-tightness. In such a sintered alloy, the alloy generally employed is one in which carbide and other alloy particles are dispersed in a pearlitic matrix or martensitic matrix.
However, a rotary compressor vane formed of the above-described sintered alloy may contain retained austenite in its metal structure upon production thereof. If the retained austenite exists in the sintered alloy vane, the retained austenite is transformed into martensite due to ambient temperature change provided by the frictional sliding motion of the vane relative to the vane groove upon operation of the compressor. This transformation causes a deformation with the passing of time together with expansion of the vane.
This change with time is disadvantagous for the vane assembled in the compressor shown in FIG. 1, since such vane requires extremely high dimensional accuracy and stability.
In order to remove the retained austenite, the sintered alloy is subjected to oil hardening or oil tempering to obtain martensitic structure. However, since the sintered product contains pores or voids, oil accumulated therein may ooze out of the sintered product. If such a sintered product is used as a vane of the rotary compressor, the oil may deteriorate the property of flon gas used as a cooling medium. This oil tempering is disclosed for example, Japanese patent Application publication (Kokai)No.56-5955.